problem 78.hs

module Main where

import Data.Map as Map

p :: (Ord a, Num t, Num a) => a -> a -> Map (a, a) t -> Map (a, a) t
p k n m = 
  if member (k, n) m then
    m
  else if k > n then
    insert (k, n) 0 m
  else if k == n then
    insert (k, n) 1 m
  else
    let a = p (k + 1) n m
        b = p k (n - k) m
    in unions [insert (k, n) ((a ! (k + 1, n)) + (b ! (k, n - k))) m, a, b]